Achievements obviously :P
I want one for doing the entire thing in heroic mode without visiting the training spot or doing a final zone battle more than once...I've nearly masterd it!
Other than that, I think it would be cool to have an option of PvP to add or remove wheel slots so you could have more/less abilities. I think the different strategys that would evolve when you only have 3 abilites/can have 20 differents types would be interesting, and could possibly mean uses for underused moves...